Liquid crystal display (LCD) devices or organic electro luminescence (EL) display devices are known as plane type display devices (flat displays). In addition, As one of the driving methods of the plane type display devices, there is an active-matrix method. In active-matrix display devices, thin film transistors (TFT) are generally used as active elements driving light emission units (light emission elements) of pixels.
As basic performances necessary in thin film transistors (which will be also described hereinafter as “TFTs” in some cases), a large driving current at the time of writing of a signal, a small leakage current at the time of retaining of a signal, and a small variation in characteristics between elements can be exemplified. On the other hand, performance values necessary in pixel control TFTs and peripheral circuit control TFTs are not necessarily the same, but there are appropriate values. Therefore, it is necessary to separately generate element characteristics between the pixel control TFTs and the peripheral circuit control TFTs. This point is also similar between TFTs when a pixel circuit is configured using the plurality of TFTs in pixels.
In the related art, element characteristics of TFTs are separately generated by changing densities of ion implantation of the TFTs between a display region in which pixels are formed and a peripheral region in which peripheral circuits are formed (for example, see Patent Literature 1).